Realizing Complete Solid-Solution Reaction in a High Sodium-Content P2-Type Cathode for High-Performance Sodium-Ion Batteries.

P2-type layered oxides suffer from ordered Na + /vacancy arrangement and P2 → O2/OP4 phase transitions, incurring them exhibit multiple voltage plateaus upon Na + extraction/insertion. The deficient sodium in P2-type cathode easily induces the terrible structural stability at deep desodiation state and limited reversible capacity during Na + de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2-type layered oxides. To migrate these challenges, we develop a novel high sodium-content (0.85) and plateau-free P2-type cathode-Na 0.85 Li 0.12 Ni 0.22 Mn 0.66 O 2 (P2-NLNMO). The complete solid solution reaction in wide voltage range ensures both small volume variation (1.7 %) and fast Na + kinetics (10 - 11 cm 2 s - 1 ). The high sodium-content P2-NLNMO exhibits a higher reversible capacity of 123.4 mA h g - 1 , superior rate capacity of 79.3 mA h g -1  at 20 C and 85.4% of capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid-solution reaction are critical to realize high-performance P2-type cathode for sodium-ion batteries.